Seal for high speed centrifuge



Dec. 17, 1957 c. w. SKARSTROM 2,813,704

SEAL FOR HIGH SPEED CENTRIFUGE Filed Aug. 29, 1942 nited States Patent SEAL FOR HIGH SPEED CENTRIFUGE Charles W. Skarstrom, Pearl River, N. Y., assignor to the United States of America as represented by the United States Atomic Energy Commission Application August 29, 1942, Serial No. 456,675

3 Claims. I l. 233-27 The present invention relates to improvements in centrifugal machines and more specifically in the construction of the bowls for centrifugal separators adapted to operate at extremely high rotational velocities. The invention will be understood from the following description and drawings.

The drawing is a sectional elevation taken along the diameter of the cylindrical bowl of the centrifuge, but showing only a portion of the side wall of the bowl and a portion of the end closure and illustrating the method of sealing the one to the other.

Centrifugal separators of the types known and used for industrial purposes at the present time operate at relatively low rotational speeds as compared to those contemplated herein and while the centrifugal force employed at the present time is many times the force of gravity, there is no great difficulty in the construction of bowls for the purposes and conditions for and under which they are now used. The bowls at present are constructed of sheet metal for low speeds and for higher speeds the side walls are usually made of seamless tubing, the ends being screwed on as caps or into the bowls as plugs. While such construction as indicated above is satisfactory for forces of the order up to about 20,000 times the force of gravity, they are quite unsatisfactory for substantially greater forces which do not permit the use of either welded, clamped or screwed joints.

Although the present inventioncan be employed for centrifuges separating liquid and solid constituents, it is designed particularly for the separation of gases and vapors and many problems'arise in such applications which are not met in other centrifugation problems. In the case of gases, for example, the materials after separation are often of extremely great value and substantially no leakage whatever can be permitted and by this is meant that the leakage must be below say one or two parts per million of the throughput. Again the force of separation required is much greater than is ordinarily employed for separating liquids or solids from liquids.

It has been demonstrated that the pressure in a rotating gas rises as an exponential'function of the distance measured radially outwardly from the axis of rotation. Because the pressure gradient is largest nearest the periphery, a seal located even to inch further radially outward from the inner edge of the bowl is subject to a greatly increased pressure. It is desirable, therefore, to locate the seal between the bowl Wall and the end plates at a point no further radially than the inner edge of the bowl wall. In the first place, the seal is not subject to any external fluid pressure greater than that existing at the bowl wall. Furthermore, in separating vapors, care must be taken to prevent condensation at the bowl periphery. While this might be done a number of ways such as careful adjustment of the centrifuge speed, adjustment of the spinning bowl temperature, regulation of the pressure existing at the axis of the bowl, if the seal is operative at a point further radially than the inner bowl wall ice there is a considerable build-up of pressure at that point and condensation may be caused at the sealing point. Because of the greater density of the liquid than the vapor, it is found that the prevention of the leaking of liquids is considerably more difficult than the leaking of gases.

One alternative lies in the shaping of the bowl in such a wag. that the side walls are not of uniform radius, but the radius is decreased and the sealing can therefore be accomplished at a radius less than the maximum interior radius of the bowl. This has disadvantages, however, in that it is difficult to provide inlet and outlet pipes. These must pass through concentric tubes or passageways in the shaft about which the bowl rotates and it is desirable to have as large a shaft as possible, since the capacity of the centrifuge is generally limited by the rate of feed and withdrawal through the shaft. For these reasons therefore it is highly desirable to produce a bowl with a uniform interior radius. The bowl walls may be constructed most simply and easily from a seamless tube. It is then required that the ends of the bowl be closed and for the reasons given before, the seal should be at no greater radius than that of the maximum internal radius of the tube.

One object of the present invention is to devise a bowl construction suitable for operation with bowls of 4 to 10" in diameter which are operated at speeds in excess of 20,000 R. P. M., say up to 60,000 R. P. M. and higher,

which conditions involve forces of from 40,000 to 200,000 or more times the force of gravity.

Another object of the invention is to devise a bowl properly sealed at the ends against leakage of gases and vapors when employed under the conditions set forth above.

Other objects of the invention will be fully understood by those skilled in the art.

Referring to the drawing, numeral 1 denotes a portion of the side wall of the centrifugal bowl which may be conveniently made from an extruded metal tube so as to be as perfectly balanced and uniform as possible. Only one side of the bowl is shown, but the center line or axis on which it rotates is marked CL. Only one end of the bowl is also shown but it will be understood that it may be closed at both ends and the same type of closure may be used as the single one shown. The end of the tube or bowl 1 is bored out or otherwise expanded to a larger internal diameter so as to leave an interior circumferential shoulder 2, the surface of which lies in the plane perpendicular to the axis CL. The end closure, only a portion of which is shown, is indicated at 3 and consists of a central disc portion 4 with an expansion portion 5 in a folded form, that is to say which appears in cross section in the shape of a hair pin or U-shape. A flange 6 is provided on the exterior edge of the closure and a sealing surface 7 on the side of the closure interior to the flange. The entire closure is preferably made integral and the exterior diameter of the sealing portion 7 is such that it will fit closely within the normal diameter of the tube or bowl 1. The diameter of the flange 6 is such that it will fit closely into the bored out portion of the tube and the flange will bear against the shoulder 2. It is preferred that this fit so tightly that it will require heating of the tube and cooling of the closure in order to permit the one to slip into the other.

The sealing portion of the closure is provided with a plurality of grooves 9, three of which are shown in the drawing. These are cut deeply, that is to say to a distance of A5" to 4 into the closure .plate and extend completely around it opposite and facing the inner surface of the bowl. They are preferably cut with uniform width, the planes of their side walls being perpendicular to the axis of the shaft. While they may have squared or rounded bottoms, they may be made with sloping sides, if desired. One such groove is sometimes sufficient but more generally it is preferred to use three. In each of the grooves a gasket is placed, preferably made of rubber or rubber-like material, which is in the shape of an annular ring and provided to substantially completely fill the groove, so that the exterior surface is flush with the surface of the closure. The closure 3 may be held in place in any desired manner, as shown on the drawing, by an annular screw member 11 which is threaded on its exterior surface at 12 and adapted to fit and engage threads 13 cut into the bored out portion of the tube 1. This member 11 may be screwed into place by a lug 14, two or more of which are spaced around the interior circumference of the ring and in being screwed into place, the screw member will bring the flange 6 tightly against the shoulder 2. If desired, a gasket 15 may be placed between the member 11 and the flange. As indicated above, other equivalent means may be used.

In further description of the apparatus, it will be understood that the bowl is mounted for rotation on a shaft or equivalent mechanism which need not be shown, and the material to be separated is preferably fed continuously to the bowl through the hollow shaft. must be ports for the withdrawal of the material separated by centrifugal force, but these are likewise omitted from the drawing because they form no essential part of the present invention.

As to the operation of the seal, it will be understood that the joint or the sealing means fulfills the requireents mentioned before. Such a joint can be made very tight with a leakage comparable to that maintained in high vacuum equipment, electronic rectifiers and the like. The seal is effected by the pressure of the rubber gaskets on the interior side of the bowl and it will be seen that the greater the centrifugal force, the greater will be the pressure between the gasket and the bowl. Under these pressures the rubber or material employed for the manufactare will flow out and assume to some extent the character of a liquid, filling the crevices between the closure and the side wall of the bowl. The s'veed of rotation and other conditi ns of operation are to be ad usted so as to produce very high pressures at the bowl wall but these will be maintained below the value causing condensation when operated with condensable gases and therefore there will be no condensation on the gasket since the pressure at that point is no greater than the maximum reached in the centrifuge. Furthermore, it will be seen that there are no unusual stresses in the bowl wall due to welding and it is permissible therefore to operate at stresses up to 75 to 80% of the yield strength of the metal in the bowl.

The bowl and the end closure will, of course, be made of materials capable of standing the operating conditions and effects of the materials processed. The gasket must be of rubber or rubber-like materials, but choice is to some extent restricted because of the nature of the materials employed. There are, however, a number of materials which have the elastic qualities similar to rubber, for example, the various so-called synthetic rubbers of the chloroprene, polyprene, Thiokol, Buna and Butyl types. The gaskets will be made of the rather soft, vulcanized rubbers. It is preferable to employ a pro-vulcanized gasket but it is also possible to employ a partially vul- Similarly there canized or a raw rubber gasket which may be vulcanized in place.

The present invention is not to be limited by any theory of its operation or to the use of any specific materials or constructional features, but only to the following claims in which it is desired to claim all novelty inherent in the invention.

I claim:

1. In a high speed centrifugal machine, a bowl having a cylindrical inner surface arranged concentrically of the rotational axis of the bowl and terminating endwise of the bowl at an internal shoulder, an end closure fitting coaxially into the bowl and having an edge flange seated against said internal shoulder and an inwardly offset peripheral surface confronting a portion of said inner cylindrical bowl surface, said peripheral surface portion of the closure having a circumferential groove therein facing said inner cylindrical bowl surface, and a gasket in said groove engaging said inner cylindrical bowl surface and operable by the action of centrifugal force thereon to effect a fluid-tight seal between said closure and said inner cylindrical surface of the bowl.

2. In a high speed centrifugal machine, a bowl having a. cylindrical inner surface arranged concentrically of the rotational axis of the bowl and terminating endwise of the bowl at an internal shoulder, an end closure fitting coaxially into the bowl and having an edge flange seated against said internal shoulder and an inwardly offset peripheral surface confronting a portion of said inner cylindrical bowl surface, said peripheral surface portion of the closure having a circumferential groove therein facing said inner cylindrical bowl surface, a gasket in said groove engaging said inner cylindrical bowl surface and operable by the action of centrifugal force thereon to effect a fluid-tight seal between said closure and said inner cylindrical surface of the bowl, and a locking member carried by said bowl securing said closure in the end of said bowl with said edge flange thereof tightly seated against said internal shoulder of the bowl.

3. In a high speed centrifugal machine, a bowl having a cylindrical inner surface arranged concentrically of the rotational axis of the bowl, an end closure fitting into the bowl coaxially therewith and having a peripheral surface confronting a portion of said inner cylindrical bowl surface, said peripheral surface of the closure having a circumferential groove therein facing said inner cylindrical bowl surface, a gasket in said groove engaging said inner cylindrical bowl surface no portion of said gasket lying at a point more remote from said rotational axis than said cylindrical surface, said gasket being operable by the action of centrifugal force thereon to efliect a fluidtight seal between said closure and said inner cylindrical surface of the bowl, and retaining means secured to the inside of the bowl and arranged to maintain the closure in position so that the gasket bears exclusively against the inner cylindrical surface of the bowl.

References Cited in the file of this patent UNITED STATES PATENTS 2,253,647 Persoons Aug. 26, 1941 2,288,638 Nazro July 7, 1942 FOREIGN PATENTS 172,482 Germany June 14, 1906 391,175 Germany Feb. 29, 1924 

